1. Field of the Invention
The present invention relates to air pumps. More specifically, the present invention relates to electrically driven, multi-stage, high-pressure, reciprocating air pumps.
2. Description of the Related Art
Simple hand operated reciprocal air pumps, such as bicycle tire pumps, have been available for several decades. A cylinder and piston within the pump provide a single-action compression system that generally dawns in ambient air on the up-stroke and then compresses the air on the down-stroke. Check valves are employed on the inlet and compressed air outlet of the pump, such that a series of reciprocal stokes can be employed to gradually build up the air pressure at the outlet, which may be connected to a pneumatic tire, a storage tank, or other air-receiving container. The compression ratio of the pump limits the maximum pressure that can be developed, which is approached asymptotically. The maximum compression ratio is dictated by the displacement ratio between the volume of the fully open cylinder on the upstroke and the fully closed cylinder on the down-stroke. More efficient versions of such pumps may be configured to compress air on both the up-stroke and the down-stroke. Such pumps are single stage pumps and typically can yield 125 psi, perhaps 250 psi in a high performance design.
There are applications that require much higher operating pressure, such as compressed air tanks used for regulated breathing, air tools, and other applications. One application where high pressure air is required is with high performance air rifles. Such rifles rival performance of light caliber firearms, and may yield muzzle velocities approaching 1200 fps. In order to achieve such velocities, an air reserve tank is coupled to the rifle that provides air pressure in the 1500 psi to 3600 psi range. Air rifle users employ manually operated reciprocal air pumps to fill such tanks. However, the high pressures needed cannot be achieved with a single stage reciprocal pump. Multi-stage pumps are needed to achieve these pressure levels. Multi-stage reciprocal air pumps are known, which can achieve compressed air outlet pressures in excess of 2000 psi. Multi-stage multi-chamber pumps generally employ plural concentric cylinders divided into plural chambers using seals of various types and pistons, with successively smaller displacement volumes that enable the inlet air to be compressed to high levels through multiple stages of compression.
As the level of compression of the outlet air rises, so too does the number of mechanical and operation issues in the design and operation of the pump. While a simple bicycle pump can function without lubrication in the presence of dust and moisture, and suffice with leather flaps for a check valves, high pressure pumps will develop a number of operational problems, and have a greatly reduced useful life in the same environment. Even considering just the ideal gas law, those skilled in the art will appreciated the highly elevated temperature rise between the inlet ambient air and the compressed outlet air in a high pressure reciprocal pump. Heat, with that addition of dust, particulate or moisture, greatly challenges the design process. Design factors quickly become critical as the target outlet pressure increases. Such design problems can be partially overcome using higher quality materials, higher performance lubricants, and tighter design specifications, however, it must be appreciated that such refinements come at increased production costs. Consumers of such pumps may be unwilling to pay the additional cost of such refinements. The inventor hereof has previously filed a co-pending patent application entitled High Pressure Air Pump on May 19, 2008, and assigned U.S. Patent Office Ser. No. 12/122,882. The reciprocating air pump of that patent application has demonstrated excellent performance and has achieved commercial success. However, during operation of the High Pressure Air Pump, it has been observed that a great number of manually driven reciprocating pump strokes are required to raise the pressure in an attached compresses air tank to a desired level, particularly during periods of time where substantial consumption of the compressed air occurs. Thus it can be appreciated that there is a need in the art for a high pressure, multiple-stage, multiple chamber reciprocal air pump that can achieve high pressure, that has an adequately long useful life, that is offered at a competitive price point so as to be desirable to consumers, but also which can be driven by a means other than manual operation.